Site Directed photoirradiation

The stability of the induced I phase at the irradiated site of polymer azobenzene LC strongly depends on temperature. At temperatures above the induced I phase disappeared and the N phase was restored after some time, which depended on temperature. At high temperatures such as 140°C, the I phase disappeared in seconds. At temperatures just above Tg the induced I phase remained fairly stable for some time, but disappeared after a prolonged time. On the other hand, at temperature below Tg the induced I phase remained unchanged even after 1 year and 6 months. The cis-trans back-isomerization took place thermally even at room temperature, and the trans-ioun was restored almost completely in 1 day. Polarized absorption spectroscopy showed that even though the trans-iorm was restored in 1 day at room temperature, orientation of the /ra 5-azobenzene mesogens was different from that of the initial state. Before photoirradiation, the azobenzenes were aligned in one direction to form uniaxial monodomain, but after photoirradiation the cw-form was produced, and N—I phase transition was induced. However, after the trans-ioim was restored thermally, the orientation... 

---